With increasing development of science and technology, a tablet computer has been introduced into the market. The tablet computer has a slim appearance similar to the exterior shape of a LCD screen. Moreover, the screen of the tablet computer is a touch screen. Through the touch screen, the user may input an instruction into the tablet computer to control operations of the tablet computer. Generally, when the user intends to input a character or a symbol into the tablet computer, an on-screen keyboard is enabled and shown on the touch screen of the tablet computer. The on-screen keyboard is a virtual keyboard simulating the real keyboard device. By touching an icon of the on-screen keyboard, a corresponding character or symbol is inputted into the tablet computer. In other words, characters or symbols may be directly inputted into the tablet computer through the on-screen keyboard without the need of using any external keyboard device.
Since the tablet computer is equipped with the touch screen, if the touch screen is damaged, the operations of the tablet computer fail to be normally handled. That is, it is very important to impart protectiveness to the touch screen. For protecting the tablet computer, a protecting device for the tablet computer is introduced into the market. FIG. 1 is a schematic perspective view illustrating a conventional protecting device for a tablet computer, in which the protecting device is in a usage status. The protecting device 1 is used for storing the tablet computer 2 therein in order to protect the tablet computer 2 and a screen 20 of the personal computer 2. As shown in FIG. 1, the protecting device 1 comprises a base 10 and an upper cover 11. The base 10 has a fixing hook 101. In case that the tablet computer 2 is placed on the base 10, the tablet computer 2 may be fixed on the base 10 through the fixing hook 101. The upper cover 11 is connected with the base 10 and rotatable relative to the base 10. In case that the upper cover 11 is rotated relative to the base 10 to define an included angle A between the upper cover 11 and the base 10, the tablet computer 2 that is fixed on the base 10 may be operated by the user (see FIG. 1). Whereas, in case that the upper cover 11 is rotated relative to the base 10 to cover the base 10, the tablet computer 2 that is fixed on the base 10 may be covered and protected by the upper cover 11 (see FIG. 2).
Although the tablet computer 2 is easily carried because it has the slim appearance and no external keyboard device is needed, there are still some drawbacks. For example, the use of the touch screen to input characters or symbols becomes hindrance for most users who are familiar with the general personal computers or notebook computers. Consequently, in many circumstances, an external keyboard device is additionally prepared and connected to the tablet computer 2. In addition, the tablet computer 2 is placed and supported on a bookshelf or any other appropriate prop stand that can support the tablet computer 2. That is, the touch screen 20 of the tablet computer 2 is usually considered as a general display screen, and the external keyboard device is used for inputting characters or symbols. Generally, the external keyboard device is connected with the tablet computer 2 through a universal serial bus (USB). Alternatively, the external keyboard device may be in communication with the tablet computer 2 through a wireless transmission module by a wireless transmission technology.
Although the external keyboard device may facilitate the user to operate the tablet computer according the usual practice of the user, there are still some drawbacks. For example, the external keyboard device and the tablet computer need to be simultaneously carried. If the external keyboard device is not simultaneously carried with the tablet computer, the user has no choice but to input characters or symbols through the on-touch keyboard of the touch screen. From the above discussions, if the user intends to operate the tablet computer according to the usual practice, the external keyboard device should be additionally carried.
Hereinafter, the structure of a conventional external keyboard device will be illustrated with reference to FIG. 3. FIG. 3 is a schematic exploded view illustrating the structure of a conventional external keyboard device. As shown in FIG. 3, the conventional external keyboard device 3 comprises plural keys 30, a supporting plate 31, a membrane switch circuit module 32, a main circuit board 33, and a base 34. For clarification and brevity, only one key 30 is shown in the drawing. Each key 30 comprises a keycap 301, a scissors-type connecting element 302, and an elastic element 303. The supporting plate 31 comprises plural supporting plate openings 311 corresponding to respective keys 30. For clarification and brevity, only one supporting plate opening 311 is shown in the drawing. The membrane switch circuit module 32 comprises an upper wiring board 321, a spacer layer 322 and a lower wiring board 323. From top to bottom, the keycap 301, the scissors-type connecting element 302, the elastic element 303, the supporting plate 31, the upper wiring board 321, the spacer layer 322, the lower wiring board 323 and the base 34 of the conventional external keyboard device 3 are sequentially shown. The main circuit board 33 is located at a side of the membrane switch circuit module 32. The upper wiring board 321 has plural upper contacts 3211 corresponding to the plural keycaps 301. The lower wiring board 323 comprises plural lower contacts 3231 corresponding to the plural upper contacts 3211. Moreover, the spacer layer 322 comprises plural perforations (not shown) corresponding to the plural upper contacts 3211.
Moreover, the conventional external keyboard device 3 further comprises a top housing (not shown). The top housing comprises plural top housing openings corresponding to the plural keycaps 301. The plural keycaps 301 are penetrated through the plural keycaps 301, the plural scissors-type connecting elements 302 and the plural elastic elements 303, so that the supporting plate 31 is covered by the top housing. Due to the structures of the plural keycaps 301, the plural scissors-type connecting elements 302 and the plural elastic elements 303, the plural keycaps 301 are exposed outside a top surface of the conventional external keyboard device 3 (i.e. a top surface of the top housing) to be depressed by the user. Generally, the altitudes of the top surfaces of the plural keycaps 301 are higher than the top surface of the conventional external keyboard device 3. In other words, the keycap 301 has the raised appearance similar to the keycap of the general key.
When one of the keycaps 301 is depressed by the user, in response to the depressing force provided by the user, the keycap 301 is moved downwardly. As the keycap 301 is moved downwardly, the corresponding scissors-type connecting element 302 is swung. Since the corresponding elastic element 303 is pushed by the keycap 301, the corresponding elastic element 303 is subjected to deformation. Under this circumstance, the deformed elastic element 301 is penetrated through the corresponding supporting plate opening 311 to press the corresponding upper contact 3211, and the upper contact 3211 is penetrated through the corresponding perforation to be contacted with the corresponding lower contact 3231. Consequently, a corresponding key signal is generated. The key signal is transmitted to the main circuit board 33, and then transmitted to a computer host (not shown), which is in communication with the conventional external keyboard device 3. According to the key signal, the computer host executes an instruction corresponding to the depressed key.
However, the way of simultaneously carrying the external keyboard device and the tablet computer is inconvenient to the user. If the user does not intend to additionally carry the external keyboard device, the user needs to directly input characters or symbols through the on-touch keyboard of the touch screen The above two approaches, however, are not user-friendly.
For solving the above drawbacks, a protecting device with a keyboard device is introduced into the market. The protecting device comprises a base and an upper cover. The keyboard device is disposed on the base. The keyboard device comprises plural keys. The upper cover is connected with the base for fixing the tablet computer thereon. In other words, the conventional external keyboard device 3 is disposed on the base. Consequently, the keyboard device for the tablet computer may be operated by the user according to the usual practice. Moreover, since the tablet computer is fixed on the upper cover, the tablet computer may be operated more easily.
However, when the protecting device with the keyboard device is in a storage status, the tablet computer and the keyboard are stacked on each other. Under this circumstance, the overall thickness of the protecting device with the keyboard device is equal to the sum of the thickness of the tablet computer, the thickness of the keyboard device and the thickness of the protecting device. Since the overall thickness is too large, the protecting device in the storage status is difficult to be carried. Generally, the thickness of the keyboard is in the range between 4 mm and 6 mm.
Therefore, there is a need of providing a slim protecting device with keys' functions in order to eliminate the above drawbacks.